Chemistry Exam

Al3+(aq) + 3e- --> Al(s) E°= -1.66 V Ag+(aq) + e- Ag(s) --> E°= +0.80 V According to the standard reduction potentials given above, what is the standard cell potential for the thermodynamically favorable reaction?

+2.46 V

M (s) + 2 Ag+ (s) --> 2 Ag (s) + M2+ (aq) E°= +3.17 V Ag+(aq) + e- --> Ag (s) E°= +0.80 V According to the information above, what is the standard reduction potential for the half reaction below? M2+(aq) + 2 e- —> M(s)

-2.37 V

HCl + NH3 --> NH4Cl When excess HCl reacts with 0.250 mol of NH3, a total of 11.0 kJ of heat energy is released. What is the value of △H in kJ/mol NH3 consumed?

-44.0

A student mixes a 100.0 mL sample of 1.0 M NaOH(aq) with a 100.0 mL sample of 1.0 M of HCl(aq) in a polystyrene container. The temperature of the solutions before mixing was 20.0 °C. If the final temperature of the mixture is 26.0 °C, what is the experimental value of △Hrxn? (Assume that the solution mixture has a specific heat of 4.2 J(g°C) and a density of 1.0 g/mL).

-50 kJ/mol

CH4(g) + 2O2(g) --> CO2(g) + 2H2O(l) △Hrxn= -889.1 kJ/mol Methane is the simplest alkane and the main component of natural gas. The relative abundance of methane makes it an attractive fuel. The balanced chemical equation for the combustion of methane is shown above. Refer to the information above and the table below to answer the question that follow. Substance △Hf (kJ/mol) H2O (l) -285.8 H2O (g) -241.8 CO2 (g) -393.3 Which of the following best represents the change in enthalpy when 96 grams of methane is consumed?

-5335 kJ

3 C2H2 (g) --> C6H6 (g) The reaction for the synthesis of hexane is shown above. Based on the data in the table below, which is the standard enthalpy change, △H°rxn for the reaction represented above? Substance △H°f C2H2(g) 230 kJ/mol C6H6(g) 83 kJ/mol

-607 kJ/mol

CH4(g) + 2O2(g) --> CO2(g) + 2H2O(l) △Hrxn= -889.1 kJ/mol Methane is the simplest alkane and the main component of natural gas. The relative abundance of methane makes it an attractive fuel. The balanced chemical equation for the combustion of methane is shown above. Refer to the information above and the table below to answer the question that follow. Substance △Hf (kJ/mol) H2O (l) -285.8 H2O (g) -241.8 CO2 (g) -393.3 Which of the following is the standard heat of formation of methane, △Hf CH4 (g), as calculated from the data above?

-75.8 kJ/mol

2H2O2 (l) + 4 MnO4 (aq) + 3 ClO2 (aq) --> 4 MnO2 (s) + 3 ClO4 (aq) + 4 OH (aq). According to the balanced equation above, how many moles of ClO2 (aq) are needed to react completely with 20 mL of 0.20 M KMnO4 solution?

0.0030 mol

How many carbon atoms are contained in 2.8 g of C2H4?

1.2 x 10^23

Under which of the following conditions of temperature and pressure would 1.0 mol of a real gas CO2 (g) behave most like an ideal gas?

100K, 0.1 atm

Which of the following ground state electron configurations represents the atom that has the lowest first-ionization energy?

1s^2 2s^2 2p^6 3s^1

Al (s) --> Al3+ (aq) + 3e Zn2+ (aq) + 2e --> Zn(s) The half-reactions for the oxidation-reduction reaction between Al(s) and Zn2+(aq) are represented above. Based on the half-reactions, what is the coefficient for Al(s) if the equation for the oxidation-reduction reaction is balanced with the smallest whole-number coefficients?

2

2 KClO3 (s) --> 2 KCl (s) + 3 O2 (g). According to the equation above, how many moles of potassium chlorate, KClO3 must be decomposed to generate 1.0 L of O2 gas at standard temperature and pressure.

2/3 (1/22.4) mol

C3H8 (g) + 4 Cl2 (g) --> C3H4Cl4 (g) + 4 HCl (g) A 6.0 mol sample of C3H8 (g) and a 20. mol sample of Cl2 (g) are placed in a previously evacuated vessel, where they react according the equation above. After one of the reactants is totally consumed, how many moles of HCl (g) have been produced?

20. mol

Element Atomic Radius First Ionization Energy Calcium 194 pm 590 kJ/mol Potassium ---------- --------- Based on periodic trends and the data in the table above, which of the following are the most probable values of the atomic radius and the first ionization energy for potassium, respectively?

242 pm, 419 kJ/mol

Which of the following pieces of laboratory glassware should be used to most accurately measure out a 25.00 mL sample of a solution?

25 mL pipet

How many protons, neutrons, and electrons are in an Fe-56 atom?

26 protons, 30 neutrons, 26 electrons

NI (s) --> NI2+ (aq) + 2e- Ag+ (aq) + e- --> Ag (s) Which of the following is the balanced net ionic equation for an oxidation-reduction reaction between Ag (aq) and NI (s) based on the half-reactions above?

2Ag (aq) + NI (s) --> 2Ag (s) + NI2+ (aq)

Which of the following has the largest positve value of △S per mole of Cl2?

2NH4Cl(s) --> N2(g) + 4 H2(g) + Cl2

H2 (g) + 1/2 O2 (g) --> H2O (l) △Hrxn= x 2 Na (s) + 1/2 O2 (g) --> Na2O (s) △Hrxn= y Na (s) + 1/2 O2 (g) + 1/2 H2 (g) --> NaOH (s) △Hrxn= z Based on the information above, what is the standard enthalpy change for the following reaction? Na2O (s) + H2O (l) --> 2NaOH (s)

2z - x - y

A coffee cup calorimeter initially contains 140g of water at 22.7°C. 4.7 g of a salt, also at 22.7°C, is added to the water and, after the salt dissolves, the final temperature is 28.0°C. Calculate the heat for the dissolving of the salt. Assume that the specific heat capacity of the solution is 4.2 J/g°C and that no heat is transferred to the surroundings or the calorimeter.

3220J of heat is absorbed

A wavelength of 510 nm corresponds to an approximate frequency of 6 x 10^14 s^-1. What is the approximate energy of one photon of this light?

4 x 10^-19 J

A student wishes to prepare 2.00 liters of 0.100-molar KIO3 (molecular weight 214). The proper procedure is to weigh out

42.8 g of KlO3 and add H2O until the final homogeneous solution has a volume of 2.00 litersIs

2 KClO3 (s) --> 2 KCl (s) + 3 O2 (g). What is the percentage yield of O2 if 12.3 g of KClO3 (molar mass 123 g) is decomposed to produce 3.2 g O2 (molar mass 32 g) according to the equation?

67%

Which of the following best describes the type of bonding in cesium chloride, CsCl(s)?

A lattice of positive and negative ions held together by electrostatic forces

A student mixes 20.0 g of white KCl crystals with distilled water in a beaker. After the mixture was stirred, no crystals are visble, and the solution is clear. After several days, all of the water evaporates and white crystals are found in the beaker. Which of the pieces of experimental evidence would best would best help the student confirm that a new compound had not been made and that only a physical change occured?

After the water had evaporated, the white crystals in the beaker have mass of 20.0 g

Al3+(aq) + 3e- --> Al(s) E°= -1.66 V Ag+(aq) + e- Ag(s) --> E°= +0.80 V Which of the following is the overall balanced, net-ionic equation for the above reaction?

Al(s) + 3 Ag+(aq) --> 3 Ag(s) + Al3+(aq)

Atoms of Mg combine with atoms of F to form a compound. Atoms of which of the following elements combine with atoms of F in the same ratio?

Ba

a 23.0 g sample of a compound contains 12.0 g of C, 3.0 g of H, and 8.0 g of O. Which of the following is the empirical formula of the compound?

C2H6O

Which of the following molecules has a dipole moment of zero?

C6H6 (benzene)

Which of the following species does not contain a pi bond?

CH4

Which of the following is a nonpolar molecule that contains polar bonds?

CO2

Equal volumes of solutions in two different vessels are represented above. If the solution represented in vessel is KCl (aq), then the solution represented in vessel 2 could be an aqueous solution of

CaCl2 with twice the molarity as the solution in vessel 1

The photoelectron spectrum of the 1s electron of two isoelectronic species, Ca^+2 and Ar, are shown above. Which of the following correctly identifies the species associated with peak X and provides a valid justicitaion?

Ca^+2, because its nucleus has two more protons than the nucleus of Ar has.

Which of the following best describes the type of bonding in a sample of gold, Au(s)?

Closely packed lattice with delocalized electrons throughout

Cu(s) + 2Ag+(aq) --> Cu2+ (aq) + 2Ag(s) If the equilibrium constant for the reaction above is 3.7 x 10^15, which of the following correctly describes the standard voltage, E°, and the standard free energy change, △G°, for the reaction.

E° is positive and △G° is negative

Half reaction E° Mg2+(aq) + 2 e- --> Mg(s) -2.37 Cr3+(aq) + 3e- --> Cr(s) -0.74 Based on the information in the table above, which of the following shows the cell potential and the Gibbs free energy change for the overall reaction that occurs in an electrolytic cell?

E°cell= -1.63 V; ∆G= +944 kJ/mol

Which of the following is the net ionic equation for the reaction between aqueous sodium fluoride and hydrochloric acid?

F (aq) + H+ (aq) --> HF (aq)

London dispersion forces are weakest for which of the following gases under the same conditions of temperature and pressure?

H2

Which of the following molecules has the largest dipole moment?

H2O

Is a strong electrolyte in aqueous solution

HBr (g)

Which of the following represents a pair of isotopes?

I. atomic number = 7, mass number = 13 II. atomic number = 7, mass number = 14

A student places a piece of I2 (s) in 50.0 mL of H2O (l), another piece of I2 (s) of the same mass in 50.0 mL of C6H14 (l), and shakes the mixtures. The results are shown above. What do the results inidcate about the intermolecular interactions of the substances?

I2 and C6H14 have similar intermolecular interactions, I2 and H2O do not.

Which of the following could be the identity of a white crystalline solid that exhibits the following properties? ** It melts at 357ºC ** It does not conduct electricity as a solid. ** It conducts electricity in an aqueous solution.

KNO3 (s)

The mass spectrum of a sample of a pure element is shown above. Based on the data, the peak at 26 amu represents an isotope of which of the following elements?

Mg with 14 neutrons

Compound Molar Mass (grams) Na2O 62.0 MgO 40.3 K2O 94.2 CaO 56.1 According to the information in the table above, a 1.00 g sample of which of the following contains the greatest mass of oxygen?

MgO

Which statement correctly compares what occurs when molecules absorb photons in the microwave region with what occurs when molecules absorb photons in the infrared region?

Microwave photons cause the molecules to increase their rotational energy states, whereas infrared photons casue molecules to increase their vibrational energy states.

A 0.10 M aqueous solution of sodium sulfate, Na2SO4, is a better conductor of electricity than a 0.10 M aqueous solution of sodium chloride, NaCl. Which of the following best explains this observation?

More moles of ions are present in a given volume of 0.10 M Na2SO4 than in the same volume of 0.10 M NaCl

Macromolecules held together with strong polar bonds

N2

Which of the following contains 1 sigma (σσ)and two pi (ππ) bonds?

N2

Which of the following represents a process in which a species is reduced?

NO3 (aq) --> NO (g)

The effective nuclear charge experienced by the outermost electron of Na is different than the effective nuclear charge experienced by the outermost electron of Ne. This difference best accounts for which of the following?

Na has a lower first ionization energy than Ne

Based on the data in the tables above, which of the following statements provides the best prediction for the boiling point of NaCl?

NaCl will have a lower boiling point tha NaF because the coulombic attractions are weaker in NaCl than in NaF

Which of the following has a bond order of two?

O2

Equal volumes of 0.2 M solutions of lead (II) nitrate and potassium bromide are combined to form lead (II) bromide as a yellow precipitate. Which of the following is the correct net ionic equation for the reaction?

Pb2+ (aq) + 2Br (aq) --> PbBr2 (s)

Select the precipitation reaction.

Pb2+ (aq) + CrO4 2- (aq) --> PbCrO4 (s)

To determine the percentage of water in a hydrated salt, at student heated a 1.2346g sample of the salt for 30 minutes; when cooled to room temperature, the sample weighted 1.1857g. After the sample was heated for an additional 10 minutes and again cooled to room temperature, the sample weighed 1.1632g. Which of the following should the student do next?

Reheat the sample until the mass is constant.

Consider atoms of the following elements. Assume that the atoms are in the ground state. The atom that contains exactly two unpaired electrons

S

In which of the following species does sulfur have the same oxidation number as it does in H2SO4?

SO2CL2

Which of the following best describes the type of bonding in a sample of CO2 (s)?CO2 (s)?

Strong multiple covalent bonds, including pi bonds

Atmospheric pressure is a potent greenhouse gas. The concentration of methane in Earth's atmosphere in 1998 , expressed as a mole of a fraction, was 1745 nmol/mol (parts per billion, ppb). By 2008, however, global methane levels, which had stayed mostly flat since 1998, had risen to 1800 nmol/mol. Which of the following best describes the type of bonding in a sample of CH4(g)?

Strong single covalent bonds

After completing an experiment to determine gravimetrically the percentage of water in a hydrate, a student reported a value of 38%. The correct value for the percentage of water in the hydrate is 51%. Which of the following is the most likely explanation for this difference?

The dehydrated sample absorbed moisture after heating.

A(g) + 2 B2(g) ⇄ D(g) △H <0 The synthesis of D(g) from A(g) and B2(g) is represented by the equation above. The value of Kc for the reaction at 483 K is 14.5. Which of the following statements is true about bond energies in this reaction?

The energy absorbed as the bonds in the reactants are broken is less than the energy released as the bonds in the product are formed.

A student places a sample of a pure metal in a crucible and heats it strongly in air. Data from the experiement are given in the table above. The final mass was determined after the sample was cooled to room temperature. Which of the following statements related to the experiement is correct?

The mass of the sample increased, so a chemical changed occured when the bonds formed between the metal and another.

Element First Ionization Energy kJ/mol Atomic Radius (pm) B 801 85 C 1086 77 N 1400 75 O 1314 73 F 1608 72 Ne 2080 70 The table above shows the first ionization energy and atomic radius of several elements. Which of the following best helps to explain the deviations of the first ionization energy of oxygen from the overall trend?

There is repulsion between paired electrons in oxygen's 2p orbitals.

Based on the ionization energies of element X given in the table above, which of the following is most likely the empirical formula of an oxide of element X? Ionization Energy kJ/mol First- 577. Second- 1816. Third- 2745. Fourth- 11577. Fifth- 14482.

X2O3

In a paper chromatography experiment, a sample of a pigment is seperated into two componets, X and Y, as shown in the figure above. The surface of the paper is moderately polar. What can be concluded about X and Y based on the experimental results?

Y is more polar X

At constant temperature, the behavior of a sample of a real gas more closely approximates that of an ideal gas as its volume is increased because the

average distance between molecules becomes greater

Using the complete photoelectron spectrum for the element above, would this element have a greater or smaller atomic size compared to its most common ion's ionic size?

greater, the element above has the valence electron in a higher energy level than its ion

The complete photoelectron spectrum for an element is shown above. Which of the following observations would provide evidence that the spectrum is consisten with the atomic model of the element?

in its compounds, the element tends to form ions with a charge of +1

A sample of a hard, solid binary compound at room temperature did not conduct electricity as a pure solid but became highly conductive when dissolved in water. Which of the following types of interactions is most likely between the particles in the substance?

ionic bonds

A student obtains a sample of a pure solid compound. In addition to Avogadro's number, which of the following must the student know in order to determine how many molecules are in the sample?

molar mass of the compound, mass of the sample

A cube of ice is added to some hot water in a rigid, insulated container, which is then sealed. There is no heat exchange with the surroundings. What has happened to the total energy and the total entropy when the system reaches equilibrium?

remains constant; increases

What is the hybridization of the carbon atoms in a molecule of ethyne, represented above?

sp

CCl4, CO2, PCl3, PCl5, SF6, Which of the following does not describe any of these molecules?

square planar

The geometry of the SO3SO3molecule is best described as

trigonal planar

When solid NH4SCN is mixed with solid Ba(OH)2 in a closed container, the temperature drops, and gas is produced. Which of the following indicates the correct signs for ∆G, ∆H, and ∆S for the process?

∆G ∆H ∆S - + +

Al3+(aq) + 3e- --> Al(s) E°= -1.66 V Ag+(aq) + e- Ag(s) --> E°= +0.80 V Which of the following is true for the galvanic cell above?

∆G° < 0 and K > 1